In recent years, devices which determine the distance and the size of objects in front of a vehicle, and which appropriately control the vehicle in accordance with this determination, have been proposed for the purpose of improving the safety of vehicle operation.
Japanese Patent Application Kokai No. Hei 7-225126 describes one example of a device for recognizing objects in front of a car appropriately. The device utilizes an optical distance measuring device consisting of two light-receiving elements, and determines whether an object whose distance has been detected is a physical object (an obstacle) or a road area (including characters or white lines on the road surface). Specifically, the device comprises a stereo camera capturing an image of an object on the road, divides the image into a plurality of windows, and calculates the distance between the stereo camera and the captured object for each window. The object in front of a car is recognized by comparing the distance with a reference distance determined for each row range of the windows.
The device disclosed in Japanese Patent Application Kokai No. Hei 7-225126 decides whether the object is a physical object or a road area based on an assumption that the road spreads horizontally ahead of the vehicle. Difference may exist between the actual road and the road estimated based on the assumption when factors such as an attachment position of the camera or an installation angle have deviated from the predetermined specification. This makes it difficult to judge whether a measured value truly represents the distance to the road and may lead to a false recognition of the object. Specifically, difference may occur in such occasions as when the vehicle is lopsided by pitching or rolling, when a vehicle travels along a hill, or when the attachment point or the installation angle of the camera has changes from the location as initially specified.